2216 Bull. Chem. Soc. Jpn., 74, No. 11 (2001)
Triplet Bis(2,6-dimethylphenyl)carbenes
1:1) to give bis(4-bromo-2,6-dimethylphenyl)methanol in 55%
yield as a white solid: mp 159.4–162.2°C; H NMR (CDCl3) δ
7.13 (s, 4 H), 6.26 (d, J = 4.95 Hz, 1 H), 2.20 (s, 12 H), 1.80 (d, J
= 4.95 Hz, 1 H); MS m/z (relative intensity) 398 (M+, 10.1), 365
(12.5), 284 (18.3), 213 (100), 185 (14.3), 106 (21.6); HRMS calcd
for C17H18OBr2 m/z 395.9724, found 395.9724.
extracted with ether, and the crude diazomethane was purified by
column chromatography (ICN alumina/hexane) at −10°C, fol-
lowed by GPC (CHCl3) to give diazobis(4-cyano-2,6-dimeth-
ylphenyl)methane in 2.3% yield as yellow solid: mp 208.9–
210.6°C; mp (decomp) 270°C; 1H NMR (CDCl3) δ 7.38 (s, 4 H),
2.11 (s, 12 H); IR (CHCl3) 2048 (CwN2) and 2224 cm−1 (CN).
Irradiation for Product Identification. In a typical run, a
solution of the diazo compound (ca. 10 mg) in solvent was placed
in a Pyrex tube and irradiated with a high-pressure, 300 W mercu-
ry lamp untill all the diazo compound was destroyed. The irradia-
tion mixture was then concentrated on a rotary evaporator below
20°C. Individual components were isolated by column chroma-
tography or by preparative TLC and identified by NMR and MS.
In this way, the following products were isolated and character-
ized.
1
Bis(4-bromo-2,6-dimethylphenyl)methanol (3.8 g, 9.6 mmol)
was added to a solution of acetic anhydride (40 mL) and pyridine
(60 mL) at 0°C, and stirred at room temperature for 12 hours. The
reaction mixture was poured into ice-water and extracted with
dichloromethane. The dichloromethane layer was washed with
10% aqueous solution of sodium hydroxide and water, and dried
over anhydrous Na2SO4. The solvent was evaporated by a rotary
evaporator and dried under vacuum to give bis(4-bromo-2,6-dime-
thylphenyl)methyl acetate in quantitative yield as a light yellowish
liquid. The acetate (4.2 g, 9.6 mmol) was treated with CuCN (1.9
g, 21.0 mmol) as described above to give bis(4-cyano-2,6-dimeth-
ylphenyl)methyl acetate in 95% yield as brownish solid. The ace-
tate was dissolved in methanol and saturated aqueous solution of
potassium carbonate at room temperature to give bis(4-cyano-2,6-
dimethylphenyl)methanol in 57% yield as yellowish solid: mp
Tetrakis(2,6-dimethylphenyl)ethylene (3a).
1H NMR
(CDCl3) δ 6.93 (t, J = 7.44 Hz, 4 H), 6.79 (d, J = 7.44 Hz, 4 H),
6.72 (d, J = 7.44 Hz, 4 H), 1.93 (s, 12 H), 1.75 (s, 12 H); MS m/z
(relative intensity) 444 (M+, 100); HRMS calcd for C34H36 m/z
444.2817, found 444.2833.
1-(2,6-Dimethylphenyl)-6-methyl-1,2-dihydrobenzocyclobu-
tene (4a). 1H NMR (CDCl3) δ 7.15 (t, J = 7.44 Hz, 1 H), 7.01-
6.92 (m, 5 H), 5.06 (bs, 1 H), 3.61 (dd, J = 5.88, 13.96 Hz, 1 H),
3.77 (dd, J = 3.31, 13.96 Hz, 1 H) 2.47 (bs, 3 H), 1.99 (s, 3 H),
1.88 (bs, 3 H); MS m/z (relative intensity) 222(M+, 4.0),
207(100), 192(82.8); HRMS calcd for C17H18 m/z 222.1409, found
222.1396.
1
240.1–242.4°C, H NMR (CDCl3) δ 7.30 (s, 4 H), 6.42 (d, J =
4.95 Hz, 1 H), 2.26 (s, 12 H), 1.99 (d, J = 4.95 Hz, 1 H); IR (KBr)
2224 cm−1; MS m/z (relative intensity) 290 (M+, 18.2), 275
(21.5), 257 (42.7), 156 (100), 132 (77.2); HRMS calcd for
C19H18N2O m/z 290.1419, found 290.1350. The methanol (300
mg, 1.0 mmol) was treated with thionyl chloride (5 mL) at room
temperature to give chlorobis(4-cyano-2,6-dimethylphenyl) meth-
ane in quantitative yield as yellow solid: 1H NMR (CDCl3) δ 7.32
(s, 4 H), 6.58 (s, 1 H), 2.35 (s, 12 H). The chloromethane (304
mg, 1.0 mmol) in dry dioxane (15 mL) was added to a mixture of
ethyl carbamate (1.8 g, 19.7 mmol), AgBF4 (0.23 g, 1.2 mmol),
and dry dioxane (5 mL) and refluxed until TLC monitoring
showed that almost all of the chloride was consumed (12 h). The
cooled reaction mixture was extracted with ether, the ethereal lay-
er was washed with water, dried over anhydrous Na2SO4, and the
solvent was evaporated by a rotary evaporator. The crude product
was purified by column chromatography (SiO2, ethyl
ether:hexane–1:1) to give ethyl N-[bis(4-cyano-2,6-dimethylphe-
nyl)methyl]carbamate in 45% as yellowish solid: mp 83.3–
85.7°C; 1H NMR (CDCl3) δ 7.29 (s, 4 H), 6.40 (d, J = 8.25 Hz, 1
H), 4.97 (d, J = 8.25 Hz, 1 H), 4,19 (q, J = 7.04 Hz, 2 H), 2.20 (s,
12 H), 1.27 (t, J = 7.04 Hz, 3 H); MS m/z (relative intensity)
361(M+, 67.6), 346(28.1), 332(63.2), 288(38.0), 257(100),
157(54.2); HRMS calcd for C22H23N3O2 m/z 361.1790, found
361.1888.
Tetrakis(2,6-dimethyl-4-t-butylphenyl)ethylene (3c).
1H
NMR (CDCl3) δ 6.74 (s, 4 H), 6.63 (s, 4 H), 1.84 (s, 12 H), 1.74
(s, 12 H), 1.20 (s, 36 H); MS m/z (relative intensity) 668 (M+,
100), 278 (16.5), 1.49 (21.3); HRMS calcd for C50H68 m/z
668.5321, found 668.5265.
4-t-Butyl-1-(4-t-butyl-2,6-dimethylphenyl)-6-methyl-1,2-di-
hydrobenzocyclobutene (4c). 1H NMR (CDCl3) δ 7.00 (s, 2 H),
6.98 (s, 2 H), 4.98 (bs, 1 H), 3.55 (dd, J = 5.70, 13.78 Hz, 1 H),
3.22 (dd, J = 3.31, 13.78 Hz, 1 H), 2.42 (bs, 3 H), 2.00 (s, 3 H),
1.96 (bs, 3 H), 1.32 (s, 9 H), 1.29 (s, 9 H); MS m/z (relative inten-
sity) 334 (M+, 23.3), 319 (100), 207 (68.6), 57 (75.5); HRMS cal-
cd for C25H34 m/z 334.2661, found 334.2632.
Tetrakis(4-methoxy-2,6-dimethylphenyl)ethylene (3d). 1H
NMR (CDCl3) δ 6.37 (s, 4 H), 6.27 (s, 4 H), 3.70 (s, 12 H), 1.92
(s, 12 H), 1.71 (s, 12 H); MS m/z (relative intensity) 546 (M+,
100), 299 (11.0), 283 (13.6); HRMS calcd for C38H44O4 m/z
564.3239, found 564.3307.
4-Methoxy-1-(4-methoxy-2,6-dimethylphenyl)-6-methyl-
1,2-dihydrobenzocyclobutene (4d).
1H NMR (CDCl3) δ 6.55
To a vigorously stirred mixture of the carbamate (160 mg, 0.4
mmol) in acetic acid (5 mL) and acetic anhydride (10 mL) at 0°C
was added a portion of NaNO2 (0.7 g, 10.2 mmol) every 5 min for
3 hours . The mixture was stirred overnight at 0°C, then poured
into ice-water and extracted with ether. The ethereal layer was
washed with a saturated aqueous solution of sodium carbonate and
water, dried over anhydrous Na2SO4, and the solvent was evapo-
rated by a rotary evaporator to give ethyl N-nitroso-N-[bis(4-cy-
ano-2,6-dimethylphenyl)methyl]carbamate in 82% yield as yel-
lowish solid: 1H NMR (CDCl3) δ 7.29 (s, 4 H), 6.83 (s, 1 H), 4.41
(q, J = 7.10 Hz, 2 H), 1.98 (s, 12 H), 1.32 (t, J = 7.10 Hz, 3 H).
To a solution of the nitroso carbamate (115 mg, 0.3 mmol) in ab-
solute THF (25 mL) at −10°C was added potassium t-butoxide
(115 mg, 1.0 mmol) at once under the atmosphere of argon. The
mixture was stirred overnight until TLC monitoring showed al-
most all of the nitroso carbamate was consumed. The mixture was
(s, 2 H), 6.52 (s, 2 H), 4.92 (bs, 1 H), 3.77 (s, 3 H), 3.70 (s, 3 H),
3.53 (dd, J = 5.70, 13.78 Hz, 1 H), 3.15 (dd, J = 3.12, 13.95 Hz,
1 H), 2.43 (bs, 3 H), 1.97 (s, 3 H), 1.88 (s, 3 H); MS m/z (relative
intensity) 282 (M+, 15.5), 267 (100), 252 (33.0); HRMS calcd for
C19H22O2 m/z 282.1620, found 282.1653.
3,6-Dimethoxy-1,4a,8-trimethyl-4a,10-dihydroanthracene
(5d). 1H NMR (CDCl3) δ 6.59 (s, 1 H), 6.56 (s, 2 H), 5.68 (s, 1
H), 4.59 (s, 1 H), 3.80 (s, 3 H), 3.58 (s, 3 H), 3.09 (d, J = 15.43
Hz, 1 H), 2.51 (d, J = 15.43 Hz, 1 H), 2.35 (s, 3 H), 2.02 (s, 3 H),
0.89 (s, 3 H).
Tetrakis(4-fluoro-2,6-dimethylphenyl)ethylene (3e).
1H
NMR (CDCl3) δ 6.56 (d, J = 11.94 Hz, 4 H), 6.47 (d, J = 11.94
Hz, 4 H), 1.92 (s, 12 H), 1.73 (s, 12 H); MS m/z (relative intensity)
516 (M+, 100); HRMS calcd for C34H32F4 m/z 516.2440, found
516.2411.
4-Fluoro-1-(4-fluoro-2,6-dimethylphenyl)-6-methyl-1,2-di-